Do conditioning focused various-sided training games prepare elite youth male soccer players for the demands of competition?

Relative metrics (i.e. distance covered per minute of match time) are regularly used to quantify soccer player movement demands. However, limited literature is available concerning the peak player demands during training. This study aimed to compare the relative and peak demands of conditioning-focused various-sided training games (VSG) to competition matches in elite youth male soccer players according to playing position. Data from twenty-nine competition matches (national) and twenty-two VSGs (small, medium, and large) were collected for twenty-three elite under-17 soccer players using 15-Hz portable global positioning system tracking devices (GPSports, Canberra, Australia). Relative player movements were reported as total distance (TD) and high-speed running distance (HSRD) (> 5.0 m/s) per minute of total playing time. Peak player movements were calculated using a 1-minute rolling epoch length, reported as the maximum TD and HSRD. Linear mixed models demonstrated interactions between VSG type and player position for relative TD (p < 0.001) and HSRD (p < 0.001), and peak TD (p = 0.010) and HSRD (p = 0.003). The relative TD of VSGs were greater than match-play for all player positions. However, only Central Defenders demonstrated similar HSRD in MSGs and LSGs compared to match-play when analysed using relative calculations. External Attackers also replicated match-play relative HSRD demands in LSGs. No VSG type was found to replicate or supersede the peak player movements of match-play across any playing position. Consequently, VSGs should be supplemented with high-speed running training to prepare players for the peak running requirements of match-play.


INTRODUCTION
Soccer is a team sport characterised by high technical and tactical demands as well as large external workloads pertaining to total distance (TD) covered and player movements at high-speed (> 5.0 m/s) [1][2][3][4]. To optimise player readiness for the rigors of match-play, knowledge of movement demands concerning positional groups is vital for coaches and practitioners to use as evidencebased parameters for training programme design and player monitoring [5][6][7]. Considerable research has investigated the difference between the physical demands of various-sided games (VSGs) and running drills as a training modality to improve player performance [8][9][10][11][12]. This research has reported that whilst VSGs are effective training modalities for technical and tactical development, running drills should be implemented when seeking to expose players to high-intensity running stimuli.
Previous research in elite youth male soccer players has primarily focused on quantifying the absolute and relative (i.e. distance covered per minute of match time) movement demands Do conditioning focused various-sided training games prepare elite youth male soccer players for the demands of competition? participated in 4-5 soccer specific on-field sessions, 1-2 strength and conditioning sessions and 1-2 competition matches per week. Players also participated in 1-2 post-match contrast water immersion recovery sessions per week either following a training session or competition match. Conditioning-focused VSGs were scheduled three days prior to competition matches once a week as per microcycle training plans designed by coaching and practitioner staff. The type of VSG employed during each microcycle was at the discretion of coaching staff. Environmental conditions, competition match and training times varied substantially throughout the data collection period in accordance with seasonal fixtures and phase of season (i.e. pre-season, competition etc.). Players were familiarised with all VSG formats and task constraints as a part of regular training instructions from coaching staff.

Procedures
Competition matches (n = 29) observed in this study were National Youth League (n = 8) and National Premier League (n = 21) fixtures.
The National Youth League is a youth professional development competition whilst the National Premier League is an adult (senior) semiprofessional competition. A 4-3-3 formation was used in all matches throughout the data collection period. Matches were played on 100 × 60 m field dimensions on natural (n = 28) and synthetic (n = 1) turf surfaces. Each match was ninety-minutes in duration, separated into two forty-five-minute halves, with any additional time determined by the match referee. All matches were played under the same competition rules, limiting each team to three substitutions and a fifteen-minute break for half time. Matches were preceded by a thirty-minute standardised warm up consisting of small-sided games (SSGs), short and intermediate length maximal sprint efforts, short and long passing, shooting, as well as dynamic stretching.
Participants were categorised according to playing position as directed by the head coach. Playing positions were CD = Central Defenders (n = 4), ED = External Defenders (n = 5), MD = Midfielders (n = 6), EA = External Attackers (n = 5) and CA = Central Attackers (n = 3). Some players featured in more than one playing practitioners adjust training sessions according to player availability, optimise player readiness and provide valid training markers for conditioning training stimuli in elite youth male soccer players [5][6][7].
A common training strategy for soccer coaches and practitioners is to prescribe VSGs as a holistic training modality to effectively address physical, technical and tactical training objectives simultaneously [7,9,10,12]. However, if the objective of conditioning training is to replicate or overload the movement demands exhibited during match-play, use of a holistic training concept that equally prioritises technical and tactical objectives could result in an inadequate stimulus to achieve conditioning objectives [7,9,10,12]. Furthermore, to ensure maximal transfer to match-day performance, the principle of specificity suggests that VSGs used in soccer conditioning training should reflect the relative field dimensions (length to width ratios) of regulation playing fields [7,9,10,12]. However, previous studies have used arbitrary field dimensions, total pitch areas (m 2 ) and relative pitch area per player sizes (m 2 ) and therefore the relationship between peak demand running metrics in VSGs utilising relative field dimensions requires further investigation [7,9,10,12]. Novel data pertaining to peak player movements during conditioning-focused various-sided training games (VSGs) and match-play can help develop age-appropriate training metrics and determine whether such training drills are valid player conditioning stimuli or if supplementary conditioning drills are required [7,9,10,12]. Thus, the aim of this study was to identify and differentiate the relative and peak player movement demands of conditioning-focused various-sided training games (VSGs) to official competition matches. This study also sought to identify the influence of player position on relative and peak movement demands. This detailed investigation is pertinent to coaches and practitioners as it may provide insight into the appropriate design of VSGs when seeking to prescribe an overload stimulus, further aiding in the optimisation of player readiness from a positional profile perspective.

Experimental approach to the problem
This study employed a longitudinal observational design using a single player cohort across a thirteen-month period in national (National Youth League) and state (National Premier League) competitions.
To achieve the study aims, the relative and peak running demands of players during competition matches and VSGs were compared. Na- Conditioning-focused VSGs were divided into three categories: Small-sided games (SSG), medium-sided games (MSG) and largesided games (LSG). The design details of each game type are provided in Table 1. The relative pitch area per player (m 2 ) for each VSG type was calculated as the total pitch area divided by the number of players. The length to width ratio of each VSG type was 5:3. This was calculated based on the length to width ratio of regulation soccer field dimensions to ensure the environment of VSGs was synonymous to match-play. Goalkeepers were present for each game type although they were excluded in the calculations when determining the relative  Table 2.   |d| ≥ 0.8 [27].

RESULTS
The difference of relative and peak TD and HSRD between playing positions and game type are outlined in Figures 1 and 2 (Figures 1, 2).

Data collection
The movement demands of players during VSGs and competition matches were captured using commercial 15-Hz portable global positioning system (GPS) tracking devices (SPI HPU, GPSports, Canberra, Australia). Players were fitted with a garment that allowed the GPS unit to be positioned between the scapulae. Each player was allocated the same GPS unit for the duration of data collection to minimise the effect of inter-unit error. After each competition match and VSG was completed, GPS data were extracted using proprietary software (Team AMS, Canberra, Australia). Each GPS file was processed to include only data captured during the VSG and competition match time (i.e. warm-up data were excluded from the analysis). To ensure satellite connectivity, GPS devices were turned on thirtyminutes before each VSG and competition match. During all competition matches and VSGs, 4-12 satellites were available for connectivity and signal transmission, satisfying the criteria for ideal positional detection [14]. Horizontal dilution of precision (HDOP) was not reported by the proprietary software (Team AMS, Canberra, Australia).
Movement demands were reported as total distance per minute (TD/min) and high-speed (> 5.0 m/s) running distance per minute (HSRD/min). The HSRD velocity threshold was chosen based on recommendations for elite youth male soccer players [3,4]. The interunit reliability, expressed as a coefficient of variation, for the GPS devices has been reported as 1.4% for total distance, 7.8% for distance at speeds between 2.0 m/s to 5.9 m/s and 4.8% for distance covered at speeds > 5.9 m/s [15]. Relative movement demands were calculated by dividing the absolute values of TD and HSRD by the duration of the competition match or VSG. To calculate peak TD and HSRD, each competition match and VSG file was split into 30 second time intervals. The rollapply function from the zoo [16] package in R version 4.0.3 [17] using RStudio version 1.4.1103 [18] was applied to calculate 1-minute rolling sums for TD and HSRD.
Peak demands were defined as the maximum TD and HSRD achieved in 1-minute. Rolling epochs were employed in this investigation as fixed epochs have been demonstrated to underestimated total (7-10%) and high-speed (12-25%) distance (defined as > 5.5 m/s) in elite senior male soccer players [6]. Furthermore, whilst the use of 1-, 2-, 5-and 10-minute rolling epochs has been utilised when determining peak running demands [6,19], the duration of 3v3 (2-min) and 5v5 (2.5-min) SSGs as well as 6v6 (5-min) MSGs in this study do not allow for 5-and 10-minute rolling epochs to be applied. As such, to allow comparison and account for the differing durations between VSGs and competition matches, 1-minute rolling epochs were employed [6,19].

Statistical analysis
Statistical analyses were conducted using R version 4.0.3 [17] in RStudio version 1.4.1103 [18]. Using the lmer function from the lme4 package [20], separate Linear Mixed Models (LMM) were ap- The least-squares mean difference of relative and peak running demands and 95% confidence interval of difference according to VSG format, not accounting for playing position are presented in Tables 3 and 4, respectively.

DISCUSSION
The aim of this study was to compare the relative and peak movement demands of conditioning-focused various-sided training games (VSGs) to official competition matches. Within this analysis we also sought to identify the influence of player position on these movement demands. The results of this study indicate that, when analysed using relative metrics, SSGs, MSGs and LSGs could be used to supersede the relative TD demands of match-play ( Figure 1). However, only Central Defenders and External Attackers were found to replicate the relative HSRD demands of match-play in LSGs (Figure 2 A, D).
In contrast, when analysed using peak metrics, no VSG type was found to replicate or supersede the peak TD and HSRD of match-play across all playing positions (Figures 1, 2) and subsequently cannot be prescribed to prepare players for the peak running requirements of competition matches.
A player's ability to produce high-speed running is paramount to gain an advantage in decisive attacking or defensive soccer situations and is considered a valid and important measure of physical performance in soccer [28,29,30]. The relative and peak HSRD observed in SSGs and MSGs were generally lower than the demands observed in matches (Figure 2). Large Sided Games elicited similar relative HSRD demands to match-play for Central Defenders and External Attackers (Figure 2 A, D) whilst External Defenders, Midfielders and Central Attackers covered slightly less relative HSRD in LSGs compared to matches. All playing positions covered less peak HSRD in SSGs,  benchmarks being questioned. Therefore, coaches and practitioners should seek to examine peak running demands as a composite construct resulting from a combination of physical, technical, tactical and contextual variables [36]. Future studies should seek to quantify such variables in addition to players internal response when analysing peak running demands in VSGs to shed further light on the practicality of VSGs for conditioning training [36]. The varying duration and training prescription between VSG types is a limitation as this may have influenced the pacing strategies of players [33]. However, it could be argued that this approach seems to have greater ecological validity as the research environment reflected the training structure implemented by coaching staff. As a longitudinal study design was employed, the influence of fitness levels and fixture congestion across different periodisation phases should be considered and analysed in future investigations. Recent research has highlighted the use of analysing peak player movement demands according to ball-in-play time periods [4] but was outside of scope of this investigation. Expansion of this research to accurately identify and record the external workloads of players during ball-in-play periods during conditioning focused VSGs and match-play would be extremely beneficial to understand the minimum effective dosage needed to achieve desired overload parameters.

CONCLUSIONS
We report on the relative and peak demands of conditioning-focused various-sided training games (VSG) in comparison to official competition matches, with consideration to the influence of player position.
Players superseded the relative total running requirements of matchplay in all VSG formats. However, only Central Defenders and External Attackers were able to replicate the relative high-speed requirements of match-play during LSGs. Furthermore, players were not able to replicate or supersede the peak total and high-speed running demands of match-play in any VSG format. Therefore, coaches and practitioners are not able to use VSGs to elicit an appropriate training stimulus to prepare players for the peak running requirements of match-play. Despite potential time constraints throughout microcycles and the efficiency of using VSGs as a training modality, coaches and practitioners are advised to implement supplementary high-speed running training to best prepare elite youth male soccer players for the peak running requirements of match-play. For example, the peak total and high-speed running metrics for match-play reported in this study could be used as benchmarks to develop position specific supplementary high-speed running training.
relative and peak HSRD in SSGs and MSGs is likely a result of decreased total and relative pitch area, reduced interpersonal distances and compact defensive behaviours, affording players less of an opportunity to perform high-speed running compared to LSGs [8,31,32]. The reduced peak HSRD recorded in LSGs compared to match-play could potentially be due to the time constraints, altering the conscious or subconscious pacing strategies of players or affording players less opportunity to be subjected to demanding phases of play [33].
To optimally prepare players for the demands of match-play, players must be exposed to high-speed running loads that surpass competition situations relative to the requirements of their position [11,28,31]. In alignment with the recommendations by Arslan et al. [10] and Köklü et al. [9] the results of this study demonstrate that supplementary high-speed running training should be prescribed and periodised appropriately in conjunction with VSGs to adequately prepare players for position-specific, match-play peak high-speed running requirements. As such, exposure to appropriate high-speed running external workloads will need to be planned for separately as selective or indicated interventions targeting either positional player subgroups or individuals who have not reached their respective required loads for physical preparation. However, this presents a scheduling challenge for coaches and practitioners, particularly if there are mid-week fixtures and off-field strength and conditioning practices to accommodate [31].
An important adjunct to this outcome is that previous research has reported that high-speed running is a modifiable risk factor for hamstring injuries [34,35]. To allow for adequate recovery and promote optimal player readiness, exposure to an overload training stimulus should occur at least 96 hours before a competition match during microcycles [31]. By scheduling supplementary high-speed running training accordingly, coaches and practitioners may reduce risk for non-contact hamstring injuries and optimise player readiness according to the requirements of relevant playing positions [31,35].
Whilst absolute and relative workload metrics can provide knowledge to coaches and practitioners, previous research has suggested that utilising 1-minute rolling epoch lengths to determine the peak movement demands provides a more meaningful understanding of the most demanding periods of match-play [5,6,11]. Moreover, when designing training drills and programmes in accordance with the principles of overload and specificity, peak movement demand metrics may provide coaches and practitioners with a more valid training marker for monitoring the intensity of their conditioning training sessions. Practically, coaches and practitioners should be aware of the differences and compare relative and peak player movement demands in VSGs and matches to help provide greater context regarding the movement demands imposed.
Whilst this study provides valuable information to coaches and practitioners, some limitations should be considered. Firstly, Novak et al. [36] recently highlighted that true peak running demands appear to be highly individual and likely occur under a multitude of conditions leading to the use of peak running metrics as training